An in vitro model for the study of human hair growth.

Human anagen hair follicles were isolated by microdissection from human scalp skin. Isolation of the hair follicles was achieved by cutting the follicle at the dermosubcutaneous fat interface using a scalpel blade. Intact hair follicles were then removed from the fat using watch makers' forceps. Isolated hair follicles maintained free floating in supplemented Williams E medium in individual wells of 24-well multiwell plates showed a significant increase in length over 4 days. The increase in length was seen to be attributed to the production of a keratinized hair shaft, and was not associated with the loss of hair follicle morphology. [Methyl-3H]thymidine autoradiography confirmed that in vitro the in vivo pattern of DNA synthesis was maintained; furthermore, [35S]methionine labeling of keratins showed that their patterns of synthesis did not change with maintenance. Serum was found to inhibit hair follicle growth in vitro; and when follicles were maintained in serum-free medium, they grew for up to 10 days, suggesting that in vitro the hair follicles are able to regulate their own growth, possibly by the production of relevant growth factors. This may prove useful in identifying the autocrine/paracrine mechanisms that operate in the hair follicle. The importance of this model to hair follicle biology is further demonstrated by the observations that TGF-beta 1 has a negative growth regulatory effect on hair follicles in vitro and that EGF and its other receptor ligand TGF-alpha mimic the in vivo depilatory effects of EGF that have been reported for sheep and mice.